Multi-loop power generation system and method using cold heat of liquefied gas

Abstract

The present invention relates to a system and a method for multi-loop power generation using cold heat of a liquefied gas, wherein power is generated by recovering waste cold heat of a liquefied gas in multiple loops. The multi-loop power generation system using cold heat of a liquefied gas according to the present invention comprises at least two refrigerant cycles including a main refrigerant cycle for recovering cold heat of a liquefied gas and an auxiliary refrigerant cycle for recovering residual cold heat of the main refrigerant. The main refrigerant cycle includes: a main refrigerant turbine-generator for generating power by driving a turbine with a main refrigerant stream; and a first main refrigerant economizer for recovering cold heat of the liquefied gas through a heat exchange between the liquefied gas and the main refrigerant stream expanded by driving the turbine. The auxiliary refrigerant cycle includes: an auxiliary refrigerant turbine-generator for generating power by driving the turbine with an auxiliary refrigerant stream; and a first auxiliary refrigerant economizer for recovering residual cold heat of the main refrigerant through a heat exchange between the auxiliary refrigerant stream expanded by driving the turbine and the main refrigerant stream which has recovered cold heat of the liquefied gas.

Description

Multi-loop power generation system and method using cold energy from liquefied gas

[0001] The present invention relates to a multi-loop power generation system and method using the cold heat of liquefied gas, which recovers the waste cold heat of liquefied gas through multiple loops and generates power.

[0002] Natural gas is liquefied at extremely low temperatures at its production site, forming liquefied natural gas (LNG). This is then transported long distances to its intended destination. Natural gas is liquefied by cooling it from atmospheric pressure to the cryogenic temperature of approximately -163°C, creating LNG. Liquid natural gas, or LNG, has a volume roughly 1 / 600th that of gaseous natural gas, making it ideal for storage and transportation.

[0003] Natural gas stored in a liquid state is regasified using a regasification facility to produce natural gas in a gaseous state, and is supplied to each demander in a gaseous state.

[0004] Basically, the regasification facility is composed of a high-pressure pump that compresses natural gas, i.e. LNG, in a liquid state stored in a storage tank to the pressure required by the demander, and a vaporizer that vaporizes the high-pressure LNG compressed by the high-pressure pump into natural gas.

[0005] Seawater, which is readily available, is primarily used as the primary heat source for vaporizing LNG in vaporizers. The cold energy of the LNG is recovered through direct or indirect heat exchange with the cold seawater, which is then discharged back into the sea.

[0006] The energy required to vaporize natural gas and undergo a phase change reaches 200 kcal per kilogram. A significant amount of energy is lost during the vaporization process, with the gas being discharged into the ocean by seawater.

[0007] Cold power generation is one of the technologies that effectively utilizes the cold energy of LNG. A typical commercial cold power generation system operates in a closed loop, where high-temperature, high-pressure gaseous refrigerant is reduced to low pressure through an expander, driving a turbine to generate electricity. The refrigerant then undergoes heat exchange with LNG, absorbing its cold energy and liquefying it. It is then pressurized through a pump, vaporized through heat exchange with seawater, and re-circulated back to the expander, a process that repeats.

[0008] A basic LNG cold-heat power generation system is composed of a vaporizer that vaporizes LNG by exchanging heat with a working fluid, a pump that pressurizes the working fluid discharged from the vaporizer after heat exchange with LNG, a heat exchanger that heat-exchanges the working fluid pressurized by the pump with a heat source, a turbine that expands the working fluid discharged from the heat exchanger after heat exchange, and a generator that generates electricity from the expansion work generated by driving the turbine.

[0009] Here, the working fluid circulates through a closed cycle consisting of a vaporizer, pump, heat exchanger, and turbine, undergoing a phase change in which it is condensed while exchanging heat with LNG in the vaporizer and vaporized while exchanging heat with seawater in the heat exchanger.

[0010] Conventional LNG cold power generation systems have the disadvantage of low power generation efficiency due to the relatively large loss caused by latent heat as the working fluid undergoes phase change, and the system becomes large due to the low density of the working fluid in the low-pressure section.

[0011] In addition, conventional LNG cold-heat power generation systems require control of the operating pressure and temperature of the cycle so that the working fluid can be completely condensed in the vaporizer and completely vaporized in the heat exchanger, and the temperature of the working fluid must be kept as low as possible to maximize the expansion ratio while maintaining a temperature above the freezing point, making control difficult and limiting improvements in efficiency.

[0012] Accordingly, the present invention aims to achieve the above-described object by providing a multi-loop power generation system utilizing the cold energy of liquefied gas, which improves the power generation efficiency of a conventional liquefied gas cold energy power generation system.

[0013] The challenges addressed by the present invention are not limited to those mentioned above. Other technical challenges not mentioned will be readily apparent to those skilled in the art, as described below.

[0014] According to one aspect of the present invention for achieving the above-described object, a multi-loop power generation system using the cold heat of liquefied gas is provided, comprising at least two refrigerant cycles, a primary refrigerant cycle in which a primary refrigerant stream circulates and recovers cold heat of liquefied gas, and an auxiliary refrigerant cycle in which an auxiliary refrigerant stream circulates and recovers residual cold heat of the primary refrigerant, wherein the primary refrigerant cycle comprises: a primary refrigerant turbine-generator that generates electric power by driving a turbine with the primary refrigerant stream; and a first primary refrigerant economizer that recovers cold heat of the liquefied gas by heat-exchanging the expanded primary refrigerant stream with the liquefied gas while driving the turbine; and wherein the auxiliary refrigerant cycle comprises: an auxiliary refrigerant turbine-generator that generates electric power by driving a turbine with the auxiliary refrigerant stream; and a first auxiliary refrigerant economizer that recovers cold heat of the liquefied gas by heat-exchanging the expanded secondary refrigerant stream with the primary refrigerant stream that has recovered cold heat of the liquefied gas while driving the turbine.

[0015] Preferably, the primary refrigerant cycle may further include a primary refrigerant branching section for branching the primary refrigerant stream into a plurality of primary refrigerant streams including a first primary refrigerant stream to be supplied to the first primary refrigerant economizer; and a second primary refrigerant economizer for cooling the second primary refrigerant stream by heat-exchanging a second primary refrigerant stream among the plurality of primary refrigerant streams with the first primary refrigerant stream cooled by heat exchange in the first primary refrigerant economizer.

[0016] Preferably, the primary refrigerant cycle may further include a first primary refrigerant compressor that compresses a first primary refrigerant stream cooled by heat exchange in the first primary refrigerant economizer and supplies the compressed stream to the second primary refrigerant economizer; a second primary refrigerant compressor that compresses a second primary refrigerant stream cooled by heat exchange in the second primary refrigerant economizer and supplies the compressed stream to the first auxiliary refrigerant economizer; and a primary refrigerant heater that heats the first primary refrigerant stream from which cold heat has been recovered by heat exchange in the second primary refrigerant economizer and the second primary refrigerant stream from which cold heat has been recovered in the first auxiliary refrigerant economizer and recirculates the heated stream to the primary refrigerant turbine-generator.

[0017] Preferably, the primary refrigerant cycle may include a primary refrigerant branching section provided upstream of the first primary refrigerant economizer and branching the primary refrigerant stream into a plurality of primary refrigerant streams, including a first primary refrigerant stream to be supplied to the first primary refrigerant economizer; and a plurality of primary refrigerant economizers provided in parallel to cool the plurality of primary refrigerant streams by direct or indirect heat exchange with the liquefied gas, and provided in one-to-one correspondence with the plurality of primary refrigerant streams, including the first primary refrigerant economizer.

[0018] Preferably, the primary refrigerant cycle further includes a plurality of primary refrigerant compressors which are provided in one-to-one correspondence with the plurality of primary refrigerant economizers and which compress one primary refrigerant stream cooled in one of the plurality of primary refrigerant economizers and supply the other primary refrigerant stream to another primary refrigerant economizer as a refrigerant for cooling the other primary refrigerant stream; and the primary refrigerant compressor provided at the last stage among the plurality of primary refrigerant compressors can supply the primary refrigerant stream cooled in the plurality of primary refrigerant economizers provided at the last stage among the plurality of primary refrigerant economizers as a refrigerant for cooling the auxiliary refrigerant stream in the first auxiliary refrigerant economizer.

[0019] Preferably, the system may further include a plurality of primary refrigerant streams from which cold heat is recovered by heat exchange in the plurality of primary refrigerant economizers, and a primary refrigerant heater that heats the primary refrigerant stream while cooling the first secondary refrigerant stream in the first secondary refrigerant economizer and recirculates the heated primary refrigerant stream to the primary refrigerant turbine-generator.

[0020] Preferably, at least one main refrigerant heater is provided, and when two or more main refrigerant heaters are provided, the heaters may be provided in series or in parallel.

[0021] Preferably, the plurality of primary refrigerant economizers and the first auxiliary refrigerant economizer may be one or more multi-stream heat exchangers.

[0022] Preferably, the auxiliary refrigerant cycle may further include an auxiliary refrigerant branching section for branching the auxiliary refrigerant stream into a plurality of auxiliary refrigerant streams including a first auxiliary refrigerant stream to be supplied to the first auxiliary refrigerant economizer; and a second auxiliary refrigerant economizer for cooling the second auxiliary refrigerant stream by heat-exchanging a second auxiliary refrigerant stream among the plurality of auxiliary refrigerant streams with the first auxiliary refrigerant stream cooled by heat exchange in the first auxiliary refrigerant economizer.

[0023] Preferably, the auxiliary refrigerant cycle may further include a first auxiliary refrigerant compressor that compresses a first auxiliary refrigerant stream cooled by heat exchange in the first auxiliary refrigerant economizer and supplies the compressed stream to the second auxiliary refrigerant economizer; a second auxiliary refrigerant compressor that compresses a second auxiliary refrigerant stream cooled by heat exchange in the second auxiliary refrigerant economizer; and an auxiliary refrigerant heater that heats the first auxiliary refrigerant stream, from which cold heat is recovered by heat exchange in the second auxiliary refrigerant economizer, and the second auxiliary refrigerant stream compressed in the second auxiliary refrigerant compressor, and recirculates the heated stream to the auxiliary refrigerant turbine-generator.

[0024] Preferably, the auxiliary refrigerant cycle may include: an auxiliary refrigerant branching section provided upstream of the first auxiliary refrigerant economizer and branching the auxiliary refrigerant stream into a plurality of auxiliary refrigerant streams, including a first auxiliary refrigerant stream to be supplied to the first auxiliary refrigerant economizer; and a plurality of auxiliary refrigerant economizers provided in parallel to cool the plurality of auxiliary refrigerant streams by direct or indirect heat exchange with a main refrigerant stream cooled by heat exchange with the liquefied gas, and provided in one-to-one correspondence with the plurality of auxiliary refrigerant streams, including the first auxiliary refrigerant economizer.

[0025] Preferably, the auxiliary refrigerant cycle may further include: a plurality of auxiliary refrigerant compressors, which are provided in one-to-one correspondence with the plurality of auxiliary refrigerant economizers, and which compress one auxiliary refrigerant stream cooled by one auxiliary refrigerant economizer among the plurality of auxiliary refrigerant economizers and supply the compressed auxiliary refrigerant stream to another auxiliary refrigerant economizer as a refrigerant for cooling the other auxiliary refrigerant stream; and an auxiliary refrigerant heater, which heats the plurality of auxiliary refrigerant streams from which cold heat has been recovered by heat exchange in the plurality of economizers and the auxiliary refrigerant stream compressed by the auxiliary refrigerant compressor provided at the last stage among the plurality of auxiliary refrigerant compressors, and recirculates the compressed auxiliary refrigerant stream to the auxiliary refrigerant turbine-generator.

[0026] Preferably, at least one auxiliary refrigerant heater is provided, and when two or more auxiliary refrigerant heaters are provided, the heaters may be provided in series or in parallel.

[0027] Preferably, the plurality of auxiliary refrigerant economizers and the first primary refrigerant economizer may be one or more multi-stream heat exchangers.

[0028] Preferably, the first primary refrigerant economizer and the first auxiliary refrigerant economizer may be a plate-type heat exchanger, a plate-fin type heat exchanger, a printed circuit board type heat exchanger, an aluminum bonded heat exchanger, or a coil wound type heat exchanger.

[0029] Preferably, the main refrigerant stream is a vaporized gas of the liquefied gas, and the auxiliary refrigerant stream may be a single or mixed substance containing a substance having a higher boiling point than the liquefied gas.

[0030] Preferably, the main refrigerant stream or the auxiliary refrigerant stream may be a single refrigerant selected from the group consisting of hydrogen, helium, nitrogen, oxygen, neon, argon, carbon compounds having 5 or fewer carbon atoms, and freon refrigerants, or a mixed refrigerant of two or more of these.

[0031] Preferably, the pressure of the main refrigerant and the auxiliary refrigerant can be maintained above the critical pressure while circulating the main refrigerant cycle and the auxiliary refrigerant cycle, respectively.

[0032] According to another aspect of the present invention for achieving the above-described object, a multi-loop power generation method using the cold heat of a liquefied gas is provided, including: a main refrigerant power generation step of generating electric power by driving a turbine with any one refrigerant among a plurality of refrigerants; a main refrigerant cold heat recovery step of recovering cold heat of the liquefied gas in multiple stages by heat-exchanging any one refrigerant expanded while driving the turbine with liquefied gas; an auxiliary refrigerant power generation step of generating electric power by driving the turbine with another refrigerant among a plurality of refrigerants; and an auxiliary refrigerant cold heat recovery step of recovering cold heat of any one refrigerant in multiple stages by heat-exchanging the other refrigerant expanded while driving the turbine with any one refrigerant cooled while recovering cold heat of the liquefied gas in the main refrigerant cold heat recovery step, thereby cooling the other refrigerant.

[0033] The multi-loop power generation system and method using the cold energy of liquefied gas according to the present invention can produce useful energy using the ultra-low temperature cold energy that is wasted without consuming fuel or causing an oxidation reaction of the fuel.

[0034] Additionally, by applying multiple loops, energy production efficiency can be further improved compared to systems applying a single loop.

[0035] In addition, by cooling the working fluid introduced into the compressor, the energy consumed for compression can be reduced, the expansion ratio can be maximized, and the system can be optimized to improve the cold energy utilization efficiency, i.e., the power generation efficiency, of the cold energy power generation system.

[0036] In addition, by branching the expanded working fluid stream from the turbine-generator, cooling some of it by recovering the cold heat of the liquefied gas in a heat exchanger and then compressing it, and cooling the remaining part by using the working fluid stream compressed after recovering the cold heat of the liquefied gas as a refrigerant and then compressing it, the working fluid before compression can be cooled using only the cold heat of the liquefied gas without having a separate cooling cycle.

[0037] Additionally, by heating the working fluid compressed in the compressor in a heater before supplying it to the turbine-generator, the expansion energy obtainable from the turbine-generator can be maximized.

[0038] In addition, since the working fluid is maintained in a supercritical state while circulating through the cycle, the system can be made smaller compared to equipment employed in conventional cold and heat power generation systems in which the working fluid undergoes a phase change based on the same capacity.

[0039] In addition, applying a multi-loop cycle can increase the overall power generation efficiency compared to applying a single-loop cycle based on the same conditions, and can also reduce installation costs (CAPEX), such as replacing compressors with pumps by replacing refrigerant according to the operating temperature.

[0040] Additionally, since low-cost refrigerants such as nitrogen can be used, operating costs (OPEX) required for refrigerant replenishment, etc. can be reduced.

[0041] The effects of the present invention are not limited to those described above. Other effects not mentioned will be readily apparent to those skilled in the art from this specification and the accompanying drawings.

[0042] FIG. 1 is a drawing schematically illustrating the basic configuration of a multi-loop power generation system using the cold energy of liquefied gas according to the first embodiment of the present invention.

[0043] FIG. 2 is a schematic diagram illustrating a multi-loop power generation system using the cold energy of liquefied gas according to a second embodiment of the present invention.

[0044] FIG. 3 is a PT diagram for explaining the phases while the refrigerant circulates through the cycle according to one embodiment of the present invention.

[0045] FIG. 4 is a schematic diagram illustrating a single loop power generation system using the cold energy of liquefied gas as a comparative example of the second embodiment of the present invention.

[0046] In order to fully understand the operational advantages of the present invention and the objects achieved by the embodiments of the present invention, reference should be made to the accompanying drawings illustrating preferred embodiments of the present invention and the contents described in the accompanying drawings.

[0047] Hereinafter, the configuration and operation of a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Here, when adding reference numerals to components in each drawing, it should be noted that, as much as possible, identical components are indicated with the same numerals even if they are shown in different drawings. In addition, the following embodiments may be modified in various other forms, and the scope of the present invention is not limited to the following embodiments.

[0048] In the embodiments of the present invention described below, the liquefied gas may be a liquefied gas that can be transported by liquefying gas at a low temperature, and may be, for example, a hydrocarbon-based liquefied gas such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, or liquefied propylene gas. Alternatively, the liquefied gas may be a non-hydrocarbon-based liquefied gas such as liquefied carbon dioxide, liquefied hydrogen, or liquefied ammonia. However, in the embodiments described below, the liquefied gas will be described using liquefied hydrogen (LH2) as an example.

[0049] In addition, the power generation system and method using the cold heat of liquefied gas according to an embodiment of the present invention described below may be applied on land where a heat exchanger for recovering the cold heat of liquefied gas is provided, such as a liquefied gas introduction terminal, a liquefied gas thermal power plant, a liquefied gas filling station, and a liquefied gas fuel-propelled mobility.

[0050] In addition, the power generation system and method using cold energy from liquefied gas according to an embodiment of the present invention, which will be described later, can also be applied to ships or ocean-going vessels. Here, the term "ship" may include all types of ships equipped with LNG regasification facilities capable of regasifying LNG and supplying it to gas demanders, including ships with self-propulsion capabilities such as LNG RVs (Regasification Vessels) and liquefied gas fuel-propelled ships, as well as offshore structures floating on the sea, such as LNG FSRUs (Floating Storage Regasification Units).

[0051]

[0052] Hereinafter, a multi-loop power generation system and method using liquefied gas cooling according to one embodiment of the present invention will be described with reference to the attached drawings.

[0053] A multi-loop power generation system using the cold heat of liquefied gas according to the present embodiment includes a multi-loop cycle including a main refrigerant cycle (100) that recovers the cold heat of liquefied hydrogen while the main refrigerant circulates, and an auxiliary refrigerant cycle (200) that recovers the remaining cold heat of the main refrigerant while the auxiliary refrigerant circulates.

[0054] In this embodiment, a dual loop cycle is provided, including two loop cycles in which different refrigerants circulate, such as a main refrigerant cycle (100) and an auxiliary refrigerant cycle (200).

[0055] However, the power generation system according to the present embodiment may be equipped with a multi-loop cycle including two or more cycles, such as a triple loop cycle including three loop cycles including a main refrigerant cycle, an auxiliary refrigerant cycle, and an additional auxiliary refrigerant cycle.

[0056] In the case of a double-loop cycle, the auxiliary refrigerant cycle recovers the remaining cold heat of the main refrigerant stream transferred from the main refrigerant cycle and cools the auxiliary refrigerant stream to generate electricity. In addition, in the case of a triple-loop cycle, the auxiliary refrigerant cycle recovers the remaining cold heat of the main refrigerant stream transferred from the main refrigerant cycle and cools the auxiliary refrigerant stream to generate electricity, and the additional auxiliary refrigerant cycle recovers the remaining cold heat of the auxiliary refrigerant stream transferred from the auxiliary refrigerant cycle and cools the additional auxiliary refrigerant stream to generate electricity.

[0057] In addition, the multi-loop cycle according to the present embodiment may include one or more turbine-generators that generate power by driving a turbine using a refrigerant circulating in each loop cycle, one or more economizers that cool the refrigerant expanded in the turbine-generator with the cold heat of liquefied hydrogen, one or more compressors that compress the refrigerant cooled in the economizer, and one or more heaters that heat the refrigerant compressed in the compressor. The refrigerant heated in the heaters may be recycled back to the turbine-generator.

[0058] Meanwhile, each loop cycle is equipped with N economizers, capable of recovering the cold energy of liquefied hydrogen across N stages. In addition, a compressor corresponding to each economizer is equipped at the rear of each of the N economizers.

[0059] When the loop cycle is equipped with N stages, each loop cycle may further include a branching portion that branches the refrigerant circulating in the cycle into N streams upstream of the economizer, and a joining portion that merges the N streams into one stream downstream of the economizer. The joining portion is not limited to joining the N streams into one stream, and the joining portion may join the N streams into a number of streams equal to the number of heaters. For example, when two heaters are equipped, the joining portion may join the N streams into two streams and supply them to each heater.

[0060] Meanwhile, the cooled refrigerant stream from the economizer of the last stage of one loop cycle is supplied to the economizer of another loop cycle to transfer cold heat, or is supplied to the heater through the junction of the loop cycles.

[0061] In addition, the branch unit may be installed downstream of the turbine-generator and upstream of the economizer, or may be installed upstream of the turbine-generator. That is, the branch unit may distribute and supply the refrigerant stream expanded from one or more turbine-generators to each economizer, or may distribute the refrigerant stream from the branch unit into N refrigerant streams and then supply them to each of N turbine-generators. When the branch unit is installed upstream of the turbine-generator, N turbine-generators may be installed in one-to-one correspondence with N economizers.

[0062] The drawing illustrates an example in which a branch is provided downstream of a turbine-generator and a refrigerant stream expanded in one turbine-generator is branched into N streams and supplied to each economizer. However, the branch may also be provided upstream of the turbine-generator and configured such that N streams are branched at the branch, and each stream is expanded in each of the N turbine-generators and then supplied to each of the N economizers.

[0063] A branch point may refer to a point where the line through which the expanded refrigerant stream flows is divided into N lines. The branch point may also be equipped with a distributor or valve.

[0064] Hereinafter, a power generation system according to one embodiment of the present invention is described as an example of a dual loop cycle including a main refrigerant cycle (100) and an auxiliary refrigerant cycle (200).

[0065] As a first embodiment, an example is described in which the main refrigerant cycle (100) is configured in two stages including two economizers (130, 140b), and the auxiliary refrigerant cycle (200) is also configured in two stages including two economizers (230, 240b).

[0066] In addition, the second embodiment is intended to explain the efficiency improvement effect of the multi-loop power generation system according to the present embodiment using simulation results, and is explained as an example in which the main refrigerant cycle (100) is configured in four stages including four economizers (130, 140b, 140c, 140d), and the auxiliary refrigerant cycle (200) is configured in seven stages including seven economizers (230, 240b, 240c, 240d, 240e, 240f, 240g).

[0067] In these embodiments, the primary and secondary refrigerants may be fluids of different materials. In describing these embodiments, the terms "primary" and "auxiliary" are merely used to distinguish between the primary and secondary refrigerants, and do not imply that one refrigerant is primarily used and the other is used as an auxiliary refrigerant.

[0068] Additionally, the operating pressure of the main refrigerant cycle and the auxiliary refrigerant cycle of the present embodiment may be 5 barg or higher or the critical pressure of the refrigerant circulating in each cycle.

[0069] The operating temperatures of the main refrigerant cycle and the auxiliary refrigerant cycle of this embodiment may be -60°C or lower or -0°C or lower.

[0070] In this embodiment, the primary refrigerant and the secondary refrigerant may be substances that do not reach the freezing point even at the point where the lowest temperature is reached during the cycle described above.

[0071] The main refrigerant and auxiliary refrigerant of the present embodiment may be a single refrigerant selected from the group consisting of hydrogen, helium, nitrogen, oxygen, neon, argon, carbon compounds having 5 or fewer carbon atoms, and freon refrigerants, or a mixed refrigerant of two or more of these.

[0072] The primary refrigerant may be a vaporization gas of a liquefied gas or a mixture containing vaporization gas of a liquefied gas, and the secondary refrigerant may be a single substance or a mixture having a boiling point higher than that of the primary refrigerant.

[0073] In this embodiment, the boil-off gas (BOG; Boil-Off Gas), i.e. hydrogen (H2), which is generated by natural vaporization of liquefied hydrogen, the liquefied gas of this embodiment, is used as a main refrigerant, or a mixed refrigerant of hydrogen and nitrogen is used, and the use of nitrogen as a single refrigerant as an auxiliary refrigerant is used as an example.

[0074] By using the evaporation gas of the liquefied gas, which is the target of cold heat recovery, as the main refrigerant, not only can the cold heat of vaporization of the liquefied gas be recovered without reaching the freezing point while the main refrigerant circulates through the main refrigerant cycle (100), but also the cost of processing the evaporation gas can be reduced and there is the advantage of easy supply.

[0075] Meanwhile, nitrogen has an extremely low freezing point of approximately -210℃ at atmospheric pressure, making it suitable for use as an auxiliary refrigerant that does not reach the freezing point while recovering the cold energy of liquefied hydrogen. Nitrogen is an inert gas readily available from air, making it inexpensive and safe. Furthermore, because it does not contain carbon, it can be vented into the air, eliminating the need for flare equipment.

[0076] In any case, when the power generation system according to the present embodiment is applied on land equipped with liquefied gas regasification facilities such as liquefied gas terminals, or when it is applied at sea equipped with liquefied gas regasification facilities such as FSRUs, equipment for generating and supplying nitrogen for the purpose of purging or maintenance of the regasification facilities is provided.

[0077] That is, if the working fluid of the power generation system according to this embodiment is used as nitrogen, the working fluid can be easily supplied even without a separate nitrogen generation / supply device, and installation and operating costs can be reduced by using the existing equipment.

[0078] In the case of a conventional cold and heat power generation system using the propane Rankine cycle (C3 Organic Rankine Cycle), propane as a refrigerant is flammable and heavier than air, which poses a risk of jet fire.

[0079] In addition, the power generation system using the Brayton Cycle (Supercritical CO2Brayton Cycle) that uses supercritical carbon dioxide as a refrigerant is not suitable for recovering cold energy because the freezing point of carbon dioxide is -78.5℃ at normal pressure, and thus freezing may occur during the heat exchange process with liquefied hydrogen at approximately -253℃.

[0080] In addition, carbon dioxide is a greenhouse gas that causes environmental pollution, is an acid gas that causes equipment corrosion, and is dangerous to the human body when exposed to a certain concentration or higher for a long period of time. In addition, in order to maintain carbon dioxide at a pressure higher than the critical pressure, the operating pressure of the system must be maintained at a high pressure environment of 200 barg or more, making it difficult to apply in practice.

[0081]

[0082] First, referring to FIG. 1, a power generation system according to a first embodiment of the present invention includes a primary refrigerant cycle (100) in which a primary refrigerant stream (HL) circulates, and an auxiliary refrigerant cycle (200) in which an auxiliary refrigerant stream (NL) circulates.

[0083] The primary refrigerant cycle (100) of the present embodiment includes a primary refrigerant turbine-generator (110) that generates power by driving a turbine using a primary refrigerant stream (HL), and a primary refrigerant branch unit (120) that branches the primary refrigerant stream (HL) expanded in the primary refrigerant turbine-generator (110) into two streams including a first primary refrigerant stream (HL1) and a second primary refrigerant stream (HL2).

[0084] The first main refrigerant stream (HL1) and the second main refrigerant stream (HL2) are names used to describe and distinguish the streams into which the main refrigerant is divided. The first main refrigerant stream (HL1) and the second main refrigerant stream (HL2) are the same substance that flows along different paths after being divided at the main refrigerant branch point, is compressed, and joins into one main refrigerant stream (HL) upstream of the main refrigerant heater (170) to circulate through the main refrigerant cycle (100).

[0085] In addition, the primary refrigerant cycle (100) of the present embodiment includes a first primary refrigerant economizer (130) that heat-exchanges liquefied hydrogen supplied through a liquefied gas line (LL) with a first primary refrigerant stream (HL1), a first primary refrigerant compressor (150a) that compresses the first primary refrigerant stream (HL1) cooled by heat-exchanging with liquefied hydrogen in the first primary refrigerant economizer (130), a second primary refrigerant economizer (140b) that heat-exchanges the first primary refrigerant stream (HL1) compressed in the first primary refrigerant compressor (150a) with a second primary refrigerant stream (HL2), and a second primary refrigerant compressor (150b) that compresses the second primary refrigerant stream (HL2) cooled by heat-exchange with the first primary refrigerant stream (HL1) in the second primary refrigerant economizer (140b).

[0086] Meanwhile, the auxiliary refrigerant cycle (200) of the present embodiment includes an auxiliary refrigerant turbine-generator (210) that generates power by driving a turbine using an auxiliary refrigerant stream (NL), and an auxiliary refrigerant branch unit (220) that branches the auxiliary refrigerant stream (NL) expanded in the auxiliary refrigerant turbine-generator (210) into two streams including a first auxiliary refrigerant stream (NL1) and a second auxiliary refrigerant stream (NL2).

[0087] The first auxiliary refrigerant stream (NL1) and the second auxiliary refrigerant stream (NL2) are names used to distinguish and describe the streams into which the auxiliary refrigerant is divided. The first auxiliary refrigerant stream (NL1) and the second auxiliary refrigerant stream (NL2) are the same substance that circulates in the auxiliary refrigerant cycle, is compressed after being divided at the auxiliary refrigerant branching section, flows through different paths, and joins into one auxiliary refrigerant stream (NL) upstream of the auxiliary refrigerant heater (270).

[0088] In addition, the auxiliary refrigerant cycle (200) of the present embodiment comprises a first auxiliary refrigerant economizer (230) that heat-exchanges the second main refrigerant stream (HL2) compressed in the second main refrigerant compressor (150b) after being cooled by heat exchange in the second main refrigerant economizer (140b), which is the last stage economizer of the main refrigerant cycle (100), and the first auxiliary refrigerant stream (NL1), a first auxiliary refrigerant compressor (250a) that compresses the first auxiliary refrigerant stream (NL1) cooled while heat-exchanging with the second main refrigerant stream (HL2) in the first auxiliary refrigerant economizer (230), a second auxiliary refrigerant economizer (240b) that heat-exchanges the second auxiliary refrigerant stream (NL2) and the first auxiliary refrigerant stream (NL1) compressed in the first auxiliary refrigerant compressor (250a), and a second auxiliary refrigerant It includes a second auxiliary refrigerant compressor (250b) that compresses a second auxiliary refrigerant stream (NL2) cooled by heat exchange with a first auxiliary refrigerant stream (NL1) in an economizer (240b).

[0089] The primary refrigerant cycle (100) further includes a primary refrigerant heater (170) that heats a first primary refrigerant stream (HL1) heated by heat exchange in a second primary refrigerant economizer (140b) and a second primary refrigerant stream (HL2) heated while transferring cold heat to the first secondary refrigerant stream (NL1) in a first secondary refrigerant economizer (230).

[0090] In addition, the primary refrigerant cycle (100) may further include a primary refrigerant combining unit (160) provided upstream of the primary refrigerant heater (170) and combining the first primary refrigerant stream (HL1) heated in the second primary refrigerant economizer (140b) and the second primary refrigerant stream (HL2) heated in the first auxiliary refrigerant economizer (230) into one primary refrigerant stream (HL).

[0091] The main refrigerant stream (HL) heated in the main refrigerant heater (170) can be circulated back to the main refrigerant turbine-generator (110).

[0092] The auxiliary refrigerant cycle (200) further includes an auxiliary refrigerant heater (270) that heats a first auxiliary refrigerant stream (NL1) heated by heat exchange in a second auxiliary refrigerant economizer (240b) and a second auxiliary refrigerant stream (NL2) compressed in a second auxiliary refrigerant compressor (250b).

[0093] In addition, the auxiliary refrigerant cycle (200) is provided upstream of the auxiliary refrigerant heater (270) and may further include an auxiliary refrigerant combining unit (260) that combines a first auxiliary refrigerant stream (NL1) heated in a second auxiliary refrigerant economizer (240b) and a second auxiliary refrigerant stream (NL2) compressed in a second auxiliary refrigerant compressor (250b) into one auxiliary refrigerant stream (NL).

[0094] The auxiliary refrigerant stream (NL) heated in the auxiliary refrigerant heater (270) can be circulated back to the auxiliary refrigerant turbine-generator (210).

[0095] The heat source for heating the main refrigerant stream (HL) in the main refrigerant heater (170) and the heat source for heating the auxiliary refrigerant stream (NL) in the auxiliary refrigerant heater (270) may be seawater, combustion gas, or the atmosphere, but are not limited thereto.

[0096] The drawing illustrates an example in which one main refrigerant heater (170) is provided in the main refrigerant cycle (100) and one auxiliary refrigerant heater (270) is provided in the auxiliary refrigerant cycle (200). However, this is not limited thereto, and one or more of the main refrigerant heaters (170) and the auxiliary refrigerant heaters (270) may be provided in series or in parallel.

[0097] For example, two main refrigerant heaters (170) are installed in series, and the main refrigerant streams that have been branched into multiple flows are combined into one main refrigerant stream (HL) at a junction, and can be heated in two stages while sequentially passing through the two main refrigerant heaters (170) connected in series.

[0098] As another example, two primary refrigerant heaters (170) may be installed in parallel, and the primary refrigerant streams that were branched into multiple flows may be combined into two primary refrigerant streams at a junction, and the two combined primary refrigerant streams may be distributed and supplied to two primary refrigerant heaters (170) installed in parallel.

[0099] The economizers (130, 140b, 230, 240b) according to the present embodiment may each be a plate type heat exchanger, a plate-fin type heat exchanger, a printed circuit board type heat exchanger (PCHE), a brazed aluminum heat exchanger (BAHX), or a coil-wound heat exchanger (CWHX).

[0100] The drawing illustrates an example in which a first main refrigerant economizer (130) and a second main refrigerant economizer (140b) are respectively provided, but the first main refrigerant economizer (130) and the second main refrigerant economizer (140b) may be provided as a multi-stream heat exchanger as one or more cold boxes.

[0101] Additionally, all economizers, including the first main refrigerant economizer (130), the second main refrigerant economizer (140b), the first auxiliary refrigerant economizer (230), and the second auxiliary refrigerant economizer (240b), may be equipped as a multi-stream heat exchanger as one or more cold boxes.

[0102] In addition, the drawing illustrates an example in which a first auxiliary refrigerant economizer (230) and a second auxiliary refrigerant economizer (240b) are respectively provided, but the first auxiliary refrigerant economizer (230) and the second auxiliary refrigerant economizer (240b) may be provided as a multi-stream heat exchanger as one or more cold boxes.

[0103] According to the present embodiment, the expanded main refrigerant stream (HL) in the main refrigerant turbine-generator (110) is branched into at least two streams including a first main refrigerant stream (HL1) and a second main refrigerant stream (HL2), and a second main refrigerant economizer (140b) is provided downstream of the first main refrigerant economizer (130) to further recover the remaining cold heat of the first main refrigerant stream (HL1) from which cold heat is recovered from liquefied hydrogen in the first main refrigerant economizer (130), thereby increasing the flow rate of the circulating refrigerant and increasing the amount of electricity produced by the turbine.

[0104] In addition, if the cold heat of the liquefied hydrogen is recovered in multiple stages in the main refrigerant cycle (100) using the main refrigerant, and the remaining cold heat of the main refrigerant is further recovered in multiple stages in the auxiliary refrigerant cycle (200) using the auxiliary refrigerant, the number of equipment can be further increased, but the amount of power generated from the turbine-generator is greater than the amount of power consumption required to operate the increased number of equipment such as the compressor, and as a result, the power generation efficiency is improved.

[0105] As the temperature of the fluid decreases, its density increases, which reduces the compression work, so the expansion energy generated increases compared to the compression energy consumed, allowing for maximum power generation.

[0106] In this embodiment, the primary refrigerant and auxiliary refrigerant are designed so that the pressure does not fall below or below the critical pressure during the primary refrigerant cycle and auxiliary refrigerant cycle, respectively. In other words, no phase change occurs in the primary refrigerant and auxiliary refrigerant during the cycle, regardless of the temperature.

[0107] Referring to Figure 3, the primary refrigerant and auxiliary refrigerant remain in the critical region (CA) where the pressure is maintained above the critical pressure during each cycle, and therefore the phase of the primary refrigerant and auxiliary refrigerant becomes a compressible fluid or a supercritical fluid.

[0108] Since the primary and secondary refrigerants are maintained above the critical pressure during each cycle, the pinch point of the heat exchanger, i.e., the economizer (130, 140b, 230, 240b), where the primary and secondary refrigerants exchange heat, does not exist inside the device, or at least the effect occurs at a low temperature near the end of the heat exchanger, thereby maximizing heat exchange performance. In addition, since no slugging occurs, there is almost no piping stress applied to the piping through which the working fluid flows.

[0109] Additionally, in this embodiment, the main refrigerant and auxiliary refrigerant may be maintained in a supercritical state during each cycle.

[0110] If the primary and secondary refrigerants are maintained in a supercritical state while circulating each cycle according to the present embodiment, the primary and secondary refrigerants flow in a high density state, so the size of the power generation system can be made small.

[0111] Meanwhile, the lower the temperature of the fluid, the higher its density, so the energy consumed for compression decreases.

[0112] According to the present embodiment, the refrigerant stream (HL, NL) discharged from the turbine-generator (110, 210) is divided into two or more flows at a branching section, cooled in an economizer (130, 140b, 230, 240b), and then compressed in a compressor (150a, 150b, 250a, 250b), thereby reducing the energy consumed for compression.

[0113] Meanwhile, the higher the temperature of the fluid introduced into the turbine, the more energy is generated by expansion.

[0114] According to the present embodiment, by providing a heater (160, 260), the refrigerant stream (HL, NL) compressed in the compressor (150a, 150b, 250a, 250b) is heated and then supplied to the turbine-generator (110, 210) before being supplied, thereby increasing the energy generated by expansion, i.e., the amount of power generated.

[0115]

[0116] Referring to Fig. 2, in the case of a power generation system with a total of 11 stages, in which the hydrogen package of HYSYS (ver. 14) is applied, the liquefied gas is liquefied hydrogen, the main refrigerant is hydrogen evaporation gas, the auxiliary refrigerant is nitrogen, the main refrigerant cycle is a 4-stage process including 4 economizers to recover the cold heat of the liquefied hydrogen, and the auxiliary refrigerant cycle is a 7-stage process including 7 economizers to recover the remaining cold heat of the main refrigerant, it was confirmed that the efficiency was improved by approximately 8% compared to the process of recovering the cold heat of the liquefied hydrogen using a single 6-stage cycle of the main refrigerant (see Fig. 4).

[0117] Hereinafter, the simulation results will be described in more detail with reference to the second embodiment of the present invention illustrated in FIG. 2 and the power generation system having a single loop cycle illustrated in FIG. 4.

[0118] The first embodiment described above was a dual loop power generation system including a two-stage primary refrigerant cycle (100) including two economizers (130, 140b) and in which hydrogen circulates as a refrigerant for recovering the cold heat of liquefied hydrogen, and a two-stage secondary refrigerant cycle (200) including two economizers (230, 240b) and in which nitrogen circulates as a refrigerant for recovering the cold heat of liquefied hydrogen using the primary refrigerant as a medium.

[0119] The second embodiment described below is a modified example of the first embodiment, and is different in that it is a dual loop power generation system in which the main refrigerant cycle (100) is a four-stage cycle including four economizers (130, 140b, 140c, 140d), and the auxiliary refrigerant cycle (200) is a seven-stage cycle including seven economizers (230, 240b, 240c, 240d, 240e, 240f, 240g). Even if a specific description is omitted, the operating principle can be applied in the same way as the first embodiment described above.

[0120] The simulation was conducted based on the assumption that hydrogen (evaporation gas) at approximately 120 barg and approximately 10°C was supplied to the main refrigerant turbine-generator (110), and the turbine was driven, expanding to approximately 50 barg and approximately -46.88°C.

[0121] Hydrogen discharged from the main refrigerant turbine-generator (110) is branched into four streams including a first main refrigerant stream (HL1), a second main refrigerant stream (HL2), a third main refrigerant stream (HL3), and a fourth main refrigerant stream (HL4) at the main refrigerant branch (120).

[0122] The flow rates of the first main refrigerant stream (HL1), the second main refrigerant stream (HL2), the third main refrigerant stream (HL3), and the fourth main refrigerant stream (HL4) may be equal to each other or may be distributed differently.

[0123] The first primary refrigerant stream (HL1) is introduced into the first primary refrigerant economizer (130) and cooled by recovering the cold heat of the liquefied hydrogen through heat exchange with the liquefied hydrogen supplied through the liquefied gas line (LL).

[0124] The simulation was conducted based on the temperature of liquefied hydrogen supplied through the liquefied gas line (LL) being approximately -245.1℃ and 80 barg.

[0125] In the first primary refrigerant economizer (130), the first primary refrigerant stream (HL1) is cooled to about -236.4°C and discharged through heat exchange, and the liquefied hydrogen is heated to about -49.88°C and discharged.

[0126] The first primary refrigerant stream (HL1) cooled while recovering the cold heat of the liquefied hydrogen in the first primary refrigerant economizer (130) is compressed in the first primary refrigerant compressor (150a) and then supplied to the second primary refrigerant economizer (140b).

[0127] In the second main refrigerant economizer (140b), the second main refrigerant stream (HL2) branched from the main refrigerant branch section (120) and the first main refrigerant stream (HL1) compressed in the first main refrigerant compressor (150a) undergo heat exchange. Through heat exchange in the second main refrigerant economizer (140b), the second main refrigerant stream (HL2) is cooled to approximately -229°C, and the first main refrigerant stream (HL1) is heated to -94°C and discharged.

[0128] The second main refrigerant stream (HL2) cooled by heat exchange in the second main refrigerant economizer (140b) is compressed in the second main refrigerant compressor (150b) and then supplied to the third main refrigerant economizer (140c), and the heated first main refrigerant stream (HL1) is transferred to the main refrigerant junction (160).

[0129] In the third main refrigerant economizer (140c), the third main refrigerant stream (HL3) branched from the main refrigerant branch section (120) and the second main refrigerant stream (HL2) compressed in the second main refrigerant compressor (150b) undergo heat exchange. Through heat exchange in the third main refrigerant economizer (140c), the third main refrigerant stream (HL3) is cooled to approximately -218.8°C, and the second main refrigerant stream (HL2) is heated to -63.7°C and discharged.

[0130] The third main refrigerant stream (HL3) cooled by heat exchange in the third main refrigerant economizer (140c) is compressed in the third main refrigerant compressor (150c) and then supplied to the fourth main refrigerant economizer (140d), and the heated second main refrigerant stream (HL2) is transferred to the main refrigerant junction (160).

[0131] In the fourth main refrigerant economizer (140d), which is the last stage economizer of the main refrigerant cycle (100), heat is exchanged between the fourth main refrigerant stream (HL4) branched from the main refrigerant branch section (120) and the third main refrigerant stream (HL3) compressed in the third main refrigerant compressor (150c). Through heat exchange in the fourth main refrigerant economizer (140d), the fourth main refrigerant stream (HL4) is cooled to approximately -202.8°C, and the third main refrigerant stream (HL3) is heated to -49.88°C and discharged.

[0132] The fourth main refrigerant stream (HL4) cooled by heat exchange in the fourth main refrigerant economizer (140d) is compressed in the fourth main refrigerant compressor (150d) and then supplied to the first auxiliary refrigerant economizer (230), which is the first stage economizer of the auxiliary refrigerant cycle (200), and the heated third main refrigerant stream (HL3) is transferred to the main refrigerant junction (160).

[0133] Meanwhile, the simulation was conducted based on the assumption that a single refrigerant nitrogen of approximately 150 barg and approximately 10°C is supplied to the auxiliary refrigerant turbine-generator (210), and the nitrogen drives the turbine and expands to approximately 80 barg and approximately -33.64°C.

[0134] Nitrogen discharged from the auxiliary refrigerant turbine-generator (210) is branched into seven streams including a first auxiliary refrigerant stream (NL1), a second auxiliary refrigerant stream (NL2), a third auxiliary refrigerant stream (NL3), a fourth auxiliary refrigerant stream (NL4), a fifth auxiliary refrigerant stream (NL5), a sixth auxiliary refrigerant stream (NL6), and a seventh auxiliary refrigerant stream (NL7) in the auxiliary refrigerant branch (220).

[0135] The flow rates of the first auxiliary refrigerant stream (NL1), the second auxiliary refrigerant stream (NL2), the third auxiliary refrigerant stream (NL3), the fourth auxiliary refrigerant stream (NL4), the fifth auxiliary refrigerant stream (NL5), the sixth auxiliary refrigerant stream (NL6), and the seventh auxiliary refrigerant stream (NL7) may be the same or may be distributed differently.

[0136] The first auxiliary refrigerant stream (NL1) is introduced into the first auxiliary refrigerant economizer (230) and cooled while recovering the residual cold heat of the main refrigerant through heat exchange with the fourth main refrigerant stream (HL4) compressed in the fourth main refrigerant compressor (150d).

[0137] In the first auxiliary refrigerant economizer (230), the first auxiliary refrigerant stream (NL1) can be cooled to about -177.8°C and discharged through heat exchange, and the fourth main refrigerant stream (HL4) can be heated to about -63.5°C and discharged.

[0138] The first main refrigerant stream (HL1) heated by heat exchange in the second main refrigerant economizer (140b), the second main refrigerant stream (HL2) heated by heat exchange in the third main refrigerant economizer (140c), the third main refrigerant stream (HL3) heated by heat exchange in the fourth main refrigerant economizer (140d), and the fourth main refrigerant stream (HL4) heated by heat exchange in the first auxiliary refrigerant economizer (230) are combined into the main refrigerant stream (HL) in the main refrigerant junction (160). The main refrigerant stream (HL) generated in the main refrigerant junction (260) can be heated to about 10°C in the main refrigerant heater (170) and then circulated back to the main refrigerant turbine-generator (110).

[0139] The first auxiliary refrigerant stream (NL1) cooled while recovering the residual cold heat of the main refrigerant through heat exchange with the fourth main refrigerant stream (HL4) in the first auxiliary refrigerant economizer (230) is compressed in the first auxiliary refrigerant compressor (250a) and then supplied to the second auxiliary refrigerant economizer (240b).

[0140] In the second auxiliary refrigerant economizer (240b), the second auxiliary refrigerant stream (NL2) branched from the auxiliary refrigerant branch section (220) and the first auxiliary refrigerant stream (NL1) compressed in the first auxiliary refrigerant compressor (250a) undergo heat exchange. Through heat exchange in the second auxiliary refrigerant economizer (240b), the second auxiliary refrigerant stream (NL2) is cooled to about -172°C, and the first auxiliary refrigerant stream (NL1) is heated to about -64.4°C and discharged.

[0141] The second auxiliary refrigerant stream (NL2) cooled by heat exchange in the second auxiliary refrigerant economizer (240b) is compressed in the second auxiliary refrigerant compressor (250b) and then supplied to the third auxiliary refrigerant economizer (240c), and the heated first auxiliary refrigerant stream (NL1) is transferred to the auxiliary refrigerant junction (260).

[0142] In the third auxiliary refrigerant economizer (240c), the third auxiliary refrigerant stream (NL3) branched from the auxiliary refrigerant branch section (220) and the second auxiliary refrigerant stream (NL2) compressed in the second auxiliary refrigerant compressor (250b) exchange heat. Through heat exchange in the third auxiliary refrigerant economizer (240c), the third auxiliary refrigerant stream (NL3) is cooled to about -167.4°C, and the second auxiliary refrigerant stream (NL2) is heated to about -65.5°C and discharged.

[0143] The third auxiliary refrigerant stream (NL3) cooled by heat exchange in the third auxiliary refrigerant economizer (240c) is compressed in the third auxiliary refrigerant compressor (250c) and then supplied to the fourth auxiliary refrigerant economizer (240d), and the heated second auxiliary refrigerant stream (NL2) is transferred to the auxiliary refrigerant junction (260).

[0144] In the fourth auxiliary refrigerant economizer (240d), the fourth auxiliary refrigerant stream (NL4) branched from the auxiliary refrigerant branch section (220) and the third auxiliary refrigerant stream (NL3) compressed in the third auxiliary refrigerant compressor (250c) exchange heat. Through heat exchange in the fourth auxiliary refrigerant economizer (240d), the fourth auxiliary refrigerant stream (NL4) is cooled to approximately -161.8°C, and the third auxiliary refrigerant stream (NL3) is heated to approximately -67.5°C and discharged.

[0145] The fourth auxiliary refrigerant stream (NL4) cooled by heat exchange in the fourth auxiliary refrigerant economizer (240d) is compressed in the fourth auxiliary refrigerant compressor (250d) and then supplied to the fifth auxiliary refrigerant economizer (240e), and the heated third auxiliary refrigerant stream (NL3) is transferred to the auxiliary refrigerant junction (260).

[0146] In the fifth auxiliary refrigerant economizer (240e), the fifth auxiliary refrigerant stream (NL5) branched from the auxiliary refrigerant branch section (220) and the fourth auxiliary refrigerant stream (NL4) compressed in the fourth auxiliary refrigerant compressor (250d) exchange heat. Through heat exchange in the fifth auxiliary refrigerant economizer (240e), the fifth auxiliary refrigerant stream (NL5) is cooled to about -155.8°C, and the fourth auxiliary refrigerant stream (NL4) is heated to about -69°C and discharged.

[0147] The fifth auxiliary refrigerant stream (NL5) cooled by heat exchange in the fifth auxiliary refrigerant economizer (240e) is compressed in the fifth auxiliary refrigerant compressor (250e) and then supplied to the sixth auxiliary refrigerant economizer (240f), and the heated fourth auxiliary refrigerant stream (NL4) is transferred to the auxiliary refrigerant junction (260).

[0148] In the sixth auxiliary refrigerant economizer (240f), the sixth auxiliary refrigerant stream (NL6) branched from the auxiliary refrigerant branch section (220) and the fifth auxiliary refrigerant stream (NL5) compressed in the fifth auxiliary refrigerant compressor (250e) exchange heat. Through heat exchange in the sixth auxiliary refrigerant economizer (240f), the sixth auxiliary refrigerant stream (NL6) is cooled to about -148.7°C, and the fifth auxiliary refrigerant stream (NL5) is heated to about -71.8°C and discharged.

[0149] The sixth auxiliary refrigerant stream (NL6) cooled by heat exchange in the sixth auxiliary refrigerant economizer (240f) is compressed in the sixth auxiliary refrigerant compressor (250f) and then supplied to the seventh auxiliary refrigerant economizer (240g), and the heated fifth auxiliary refrigerant stream (NL5) is transferred to the auxiliary refrigerant junction (260).

[0150] In the seventh auxiliary refrigerant economizer (240g), which is the last stage economizer of the auxiliary refrigerant cycle (200), heat is exchanged between the seventh auxiliary refrigerant stream (NL7) branched from the auxiliary refrigerant branch section (220) and the sixth auxiliary refrigerant stream (NL6) compressed in the sixth auxiliary refrigerant compressor (250f). Through heat exchange in the seventh auxiliary refrigerant economizer (240g), the seventh auxiliary refrigerant stream (NL7) is cooled to about -140.8°C, and the sixth auxiliary refrigerant stream (NL6) is heated to about -75°C and discharged.

[0151] The seventh auxiliary refrigerant stream (NL7) cooled by heat exchange in the seventh auxiliary refrigerant economizer (240g) is compressed in the seventh auxiliary refrigerant compressor (250g) and then transferred to the auxiliary refrigerant junction (260).

[0152] A first auxiliary refrigerant stream (NL1) heated by heat exchange in a second auxiliary refrigerant economizer (240b), a second auxiliary refrigerant stream (NL2) heated by heat exchange in a third auxiliary refrigerant economizer (240c), a third auxiliary refrigerant stream (NL3) heated by heat exchange in a fourth auxiliary refrigerant economizer (240d), a fourth auxiliary refrigerant stream (NL4) heated by heat exchange in a fifth auxiliary refrigerant economizer (240e), a fifth auxiliary refrigerant stream (NL5) heated by heat exchange in a sixth auxiliary refrigerant economizer (240f), a sixth auxiliary refrigerant stream (NL6) heated by heat exchange in a seventh auxiliary refrigerant economizer (240g), and a seventh auxiliary refrigerant stream (NL7) cooled by heat exchange in a seventh auxiliary refrigerant economizer (240g) are auxiliary refrigerants. It is joined to the auxiliary refrigerant stream (NL) at the junction (260). The auxiliary refrigerant stream (NL) generated at the auxiliary refrigerant junction (260) can be heated to about 10°C in the auxiliary refrigerant heater (270) and then circulated back to the auxiliary refrigerant turbine-generator (210).

[0153] As a result of the simulation, the total net power generation was confirmed to be 779.3 kW per ton / hr of liquid hydrogen by subtracting the power consumed by the first main refrigerant compressor (150a), the second main refrigerant compressor (150b), the third main refrigerant compressor (150c), the fourth main refrigerant compressor (150d), the first auxiliary refrigerant compressor (250a), the second auxiliary refrigerant compressor (250b), the third auxiliary refrigerant compressor (250c), the fourth auxiliary refrigerant compressor (250d), the fifth auxiliary refrigerant compressor (250e), the sixth auxiliary refrigerant compressor (250f), and the seventh auxiliary refrigerant compressor (250g) from the sum of the power generated by the main refrigerant turbine-generator (110) and the power generated by the auxiliary refrigerant turbine-generator (210).

[0154] The single loop power generation cycle illustrated in Fig. 4 is a six-stage hydrogen (evaporation gas) cycle including a first-stage economizer (EC1) to a sixth-stage economizer (EC6), as a comparative example of the present embodiment, and the simulation was conducted based on the assumption that hydrogen (evaporation gas) of about 120 barg and about 10°C was supplied to the turbine-generator (TG) and expanded to about 50 barg and about -46.88°C while driving the turbine, as in the present embodiment described above.

[0155] According to a comparative example, hydrogen discharged from a turbine-generator (TG) is branched into six streams from a first stream (S1) to a sixth stream (S6) at a branch section (BR).

[0156] In the same manner, the first stream (S1) is cooled to about -236.4°C by heat exchange with liquefied hydrogen at about -245.1°C and 80 barg in the first economizer (EC1), and the liquefied hydrogen is heated to about -49.88°C and discharged.

[0157] The first stream (S1) cooled in the first economizer (EC1) is compressed in the first compressor (C1) and then supplied to the second economizer (EC2). In the second economizer (EC2), the first stream (S1) compressed in the first compressor (C1) and the second stream (S2) branched from the branch section (BR) undergo heat exchange, so that the second stream (S2) is cooled and the first stream (S1) is heated.

[0158] The second stream (S2) cooled in the second economizer (EC2) is compressed in the second compressor (C2) and then supplied to the third economizer (EC3), and the heated first stream (S1) is combined in the junction (CB).

[0159] In the same manner, the stream (S) generated by the first stream (S1) to the sixth stream (S6) joining at the junction (CB) is heated to about 10°C in the heater (HT) and then recycled to the turbine-generator (TG).

[0160] As a result of the simulation of the comparative example, the total net power production, which is the amount of power generated by the turbine-generator (TG) through the above-described process minus the amount of power consumed by the first compressor (C1), second compressor (C2), third compressor (C3), fourth compressor (C4), fifth compressor (C5), and sixth compressor (C6), was confirmed to be 722.2 kW per 1 ton / hr of liquefied hydrogen.

[0161] That is, it was confirmed through simulation that the multi-loop power generation system according to this embodiment has an efficiency improvement effect of approximately 8% compared to the single-loop power generation system of the comparative example.

[0162] The multi-loop power generation system using the cold energy of liquefied gas according to the present embodiment illustrated in FIG. 2 is equipped with a total of 11 stages, including a main refrigerant cycle equipped with 4 stages and an auxiliary refrigerant cycle equipped with 7 stages, compared to the single loop power generation system equipped with 6 stages illustrated in FIG. 4, so the total number of stages increases.

[0163] In terms of initial installation cost (CAPEX), the single-loop power generation system illustrated in FIG. 4 has six stages, i.e., six compressors that compress the refrigerant circulating in the cycle into a gas phase. On the other hand, the multi-loop power generation system according to the present embodiment illustrated in FIG. 2 can adopt a pump, which is cheaper than a compressor, as a means of compressing the refrigerant since the auxiliary refrigerant circulates in a critical state close to a liquid phase in the auxiliary refrigerant cycle (200).

[0164] That is, in this embodiment, the main refrigerant cycle (100) has four stages and only four compressors for compressing the main refrigerant into a gas phase are required, and the auxiliary refrigerant cycle (200) has seven stages and seven pumps are added, so as a result, capital investment costs can be reduced compared to a six-stage single-loop power generation system.

[0165] In addition, the sum of the volume flow rates of the refrigerant at the inlets of the 5-stage compressor (C5) and the 6-stage compressor (C6) of the single loop power generation system of Fig. 4 is 74.9 m 3 / h, but in the case of the multi-loop power generation system according to the present embodiment, the sum of the volume flow rates of the refrigerant at the inlet of the compressor (pump) of the auxiliary refrigerant cycle (200), i.e., the inlet volume flow rates of the compressors (pumps) of stages 5 to 11, is 26.1 m 3 / h is reduced to about 1 / 3 of the level.

[0166] For single loop power generation systems, the average density of refrigerant at the inlet of the 5th and 6th stage compressors is 11.7 kg / m 3 In contrast, the average density from stage 5 to stage 11 of the multi-loop power generation system of this embodiment is 662.2 kg / m 3 As the density increases, the heat transfer efficiency increases, so the heat exchanger area of ​​nitrogen refrigerant in a multi-loop power generation system is expected to be much smaller than in a single-loop power generation system even as the number of stages increases, thereby reducing capital investment costs (CAPEX).

[0167] From an operating expense (OPEX) perspective, using relatively inexpensive nitrogen as a refrigerant reduces operating costs, such as refrigerant replenishment due to compressor leaks. Furthermore, nitrogen is readily available, as each plant is equipped with nitrogen generation equipment and other nitrogen-operating equipment.

[0168] In terms of safety, by using an eco-friendly refrigerant that accounts for more than 78% of air rather than an explosive refrigerant, it is harmless to the human body even if it leaks, and improvements in process stability, environmental protection, and deregulation of construction are also expected.

[0169]

[0170] As described above, embodiments of the present invention have been described. It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms, in addition to the embodiments described above, without departing from the spirit or scope thereof. Therefore, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

[0171]

[0172] <Explanation of symbols>

[0173] 100: Main refrigerant cycle

[0174] 110: Main refrigerant turbine-generator

[0175] 120: Main refrigerant branch

[0176] 130, 140b, 140c, 140d: Main refrigerant economizer

[0177] 150a, 150b, 150c, 150d: Main refrigerant compressor

[0178] 160: Main refrigerant junction

[0179] 170: Main refrigerant heater

[0180] HL, HL1, HL2, HL3, HL4: Main refrigerant stream

[0181] LL: Liquefied gas line

[0182] 200: Auxiliary refrigerant cycle

[0183] 210: Auxiliary refrigerant turbine-generator

[0184] 220: Auxiliary refrigerant branch

[0185] 230, 240b, 240c, 240d, 240e, 240f, 240g: Auxiliary refrigerant economizer

[0186] 250a, 250b, 250c, 250d, 250e, 250f, 250g: Auxiliary refrigerant compressor

[0187] 260: Auxiliary refrigerant junction

[0188] 270: Auxiliary refrigerant heater

[0189] NL, NL1, NL2, NL3, NL4, NL5, NL6, NL7: Auxiliary refrigerant streams

Claims

1. At least two refrigerant cycles, including a main refrigerant cycle in which a main refrigerant stream circulates and recovers the cooling heat of liquefied gas, and an auxiliary refrigerant cycle in which an auxiliary refrigerant stream circulates and recovers the remaining cooling heat of the main refrigerant; The above main refrigerant cycle is, A primary refrigerant turbine-generator that generates electric power by driving a turbine with the primary refrigerant stream; and A first main refrigerant economizer that recovers cold heat from the liquefied gas by heat-exchanging the expanded main refrigerant stream and the liquefied gas while driving the turbine; The above auxiliary refrigerant cycle is, An auxiliary refrigerant turbine-generator that generates electric power by driving a turbine with the auxiliary refrigerant stream; and A multi-loop power generation system utilizing the cold heat of liquefied gas, comprising a first auxiliary refrigerant economizer that recovers the remaining cold heat of the main refrigerant by heat-exchanging the expanded auxiliary refrigerant stream and the main refrigerant stream from which the cold heat of the liquefied gas has been recovered while driving the turbine.

2. In claim 1, The above main refrigerant cycle is, A primary refrigerant branch unit provided upstream of the first primary refrigerant economizer and branching the primary refrigerant stream into a plurality of primary refrigerant streams, including a first primary refrigerant stream to be supplied to the first primary refrigerant economizer; and A multi-loop power generation system utilizing cold energy from liquefied gas, comprising: a plurality of primary refrigerant economizers, which are provided in parallel to cool the plurality of primary refrigerant streams by direct or indirect heat exchange with the liquefied gas, and which are provided in one-to-one correspondence with the plurality of primary refrigerant streams, including the first primary refrigerant economizer; 3. In claim 2, The above main refrigerant cycle is, It further includes a plurality of primary refrigerant compressors which are provided in one-to-one correspondence with the plurality of primary refrigerant economizers and which compress one primary refrigerant stream cooled by one of the plurality of primary refrigerant economizers and supply the compressed primary refrigerant stream to another primary refrigerant economizer as a refrigerant for cooling another primary refrigerant stream. A multi-loop power generation system utilizing the cold heat of liquefied gas, wherein the main refrigerant compressor provided at the last stage among the plurality of main refrigerant compressors supplies the main refrigerant stream cooled by the plurality of main refrigerant economizers provided at the last stage among the plurality of main refrigerant economizers as a refrigerant for cooling the auxiliary refrigerant stream in the first auxiliary refrigerant economizer.

4. In claim 2, A multi-loop power generation system utilizing cold heat from liquefied gas, further comprising: a plurality of primary refrigerant streams from which cold heat has been recovered by heat exchange in the plurality of primary refrigerant economizers; and a primary refrigerant heater for heating the primary refrigerant stream while cooling the first secondary refrigerant stream in the first secondary refrigerant economizer and recirculating the heated primary refrigerant stream to the primary refrigerant turbine-generator.

5. In claim 4, At least one of the above main refrigerant heaters is provided, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein when two or more of the above-mentioned main refrigerant heaters are provided, the heaters are provided in series or parallel.

6. In claim 2, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein the above-mentioned plurality of primary refrigerant economizers and the first auxiliary refrigerant economizer are one or more multi-stream heat exchangers.

7. In claim 1, The above auxiliary refrigerant cycle is, An auxiliary refrigerant branch unit provided upstream of the first auxiliary refrigerant economizer and branching the auxiliary refrigerant stream into a plurality of auxiliary refrigerant streams, including a first auxiliary refrigerant stream to be supplied to the first auxiliary refrigerant economizer; and A multi-loop power generation system utilizing cold energy from liquefied gas, comprising: a plurality of auxiliary refrigerant economizers, which are provided in parallel to cool the plurality of auxiliary refrigerant streams by direct or indirect heat exchange with the main refrigerant stream cooled by heat exchange with the liquefied gas, and which are provided in one-to-one correspondence with the plurality of auxiliary refrigerant streams, including the first auxiliary refrigerant economizer; 8. In claim 7, The above auxiliary refrigerant cycle is, A plurality of auxiliary refrigerant compressors are provided in one-to-one correspondence with the plurality of auxiliary refrigerant economizers, and compress one auxiliary refrigerant stream cooled by one auxiliary refrigerant economizer among the plurality of auxiliary refrigerant economizers and supply it as refrigerant to cool another auxiliary refrigerant stream to another auxiliary refrigerant economizer; and A multi-loop power generation system utilizing the cold heat of liquefied gas, further comprising: an auxiliary refrigerant heater for heating a plurality of auxiliary refrigerant streams from which cold heat has been recovered by heat exchange in the plurality of economizers, and an auxiliary refrigerant stream compressed by an auxiliary refrigerant compressor provided at the last stage among the plurality of auxiliary refrigerant compressors, and recirculating the heated auxiliary refrigerant stream to the auxiliary refrigerant turbine-generator.

9. In claim 8, At least one auxiliary refrigerant heater is provided, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein when two or more auxiliary refrigerant heaters are provided, the heaters are provided in series or parallel.

10. In claim 7, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein the above-mentioned plurality of auxiliary refrigerant economizers and the first main refrigerant economizer are one or more multi-stream heat exchangers.

11. In claim 1, A multi-loop power generation system utilizing cold energy from liquefied gas, wherein the first main refrigerant economizer and the first auxiliary refrigerant economizer are plate-type heat exchangers, plate-fin-type heat exchangers, printed circuit board-type heat exchangers, aluminum-bonded heat exchangers, or coil-wound heat exchangers.

12. In claim 1, The above main refrigerant stream is the evaporated gas of the liquefied gas, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein the auxiliary refrigerant stream is a single or mixed substance containing a substance having a higher boiling point than the liquefied gas.

13. In claim 1, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein the main refrigerant stream or the auxiliary refrigerant stream is a single refrigerant selected from the group consisting of hydrogen, helium, nitrogen, oxygen, neon, argon, carbon compounds having 5 or fewer carbon atoms, and freon refrigerants, or a mixed refrigerant comprising two or more of these.

14. In claim 1, A multi-loop power generation system utilizing the cold energy of liquefied gas, wherein the pressure of the main refrigerant and auxiliary refrigerant is maintained above the critical pressure while circulating the main refrigerant cycle and auxiliary refrigerant cycle, respectively.

15. A primary refrigerant power generation stage that generates electricity by driving a turbine with any one of a plurality of refrigerants; A main refrigerant heat recovery step for recovering the cold heat of the liquefied gas in multiple stages by heat-exchanging one of the expanded refrigerants and the liquefied gas while driving the turbine; An auxiliary refrigerant power generation step that generates electricity by driving a turbine with another refrigerant among a plurality of refrigerants; and A multi-loop power generation method using the cold heat of liquefied gas, comprising: an auxiliary refrigerant cold heat recovery step for recovering the cold heat of one refrigerant in multiple stages by exchanging heat with another refrigerant expanded while driving the turbine and one refrigerant cooled while recovering the cold heat of the liquefied gas in the main refrigerant cold heat recovery step, thereby cooling the other refrigerant.

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